Cancers of the lympho-hematopoietic system are a major cause of morbidity and mortality, with an increasing incidence of myelodysplastic syndrome and non-Hodgkins Lymphoma as the population ages and greater numbers survive prior cancers. Allogeneic hematopoietic stem cell transplant (HSCT) is curative in a proportion of patients who otherwise fail conventional chemotherapy or are known to be high risk of failure. However, this potentially life-saving procedure is restricted in its availability and is itself associated with the high risks of morbidity and mortality, primarily from immunological complications, including graft-versus-host disease (GVHD), and slow immune reconstitution. For those that survive the immediate risks of transplant therapy, relapse is still an obstacle. Toward our goal of facilitating lympho-hematopoietic recovery after umbilical cord blood (UCBT), in Project 1, we propose to 1) determine the impact of large doses of UCB CD34+ cells on the pace of immune reconstitution, 2) optimize dosing T regulatory cells for prevention of acute GVHD, and 3) optimize ex vivo expansion of thymic progenitors for accelerating immune recovery. Toward our goal of engineering a safer and more effective adoptive T cell therapy for leukemia relapse prevention and treatment, in Project 2, we propose to 1) demonstrate that drug regulated anti-hCD19SFv chimeric antigen receptor (CAR) expressing T cells can eradicate malignant CD19+ B cells, determine whether CAR persistence is dependent upon tumor- or host- derived B cell antigenic signals, and demonstrate that infusion of drug antagonists can rapidly halt CAR signaling by precluding dimerization, 2) demonstrate that human T stem-memory (Tsm) cells can be reprogrammed and genetically modified to express CARs providing self-renewable CAR-Tsm cells for adoptive tumor immunotherapy with enhanced survival, and 4) identify and validate essential regulators of the Tsm state to further optimize Tsm-based CAR therapy. And, toward our goal of engineering a safe and more effective adoptive NK cell therapy for relapse treatment, in Project 3 we propose to 1) determine the mechanism underlying the differentiation of adaptive NK cells which have potent and long-lived anti-leukemia activity, and induce their expansion in a phase I trial to eliminate leukemic blasts in patients with relapsed leukemia, and 2) optimize NK activation and tumor-targeting using bispecific killer engager (BiKE) antibodies with a subsequent 'first-in-human' clinical trial in patients with relapsed CD33+ malignancy after UCBT. Each of these strategies is highly innovative with substantial promise individually and in combination for overcoming the most important barriers - immunoincompetence and relapse - previously limiting survival as well as continuing our long-held interest in realizing the full potential of UCB in transplant medicine.